In the combustion process of a steam generator the fuel is prepared in a first stage (e.g. pulverizing of the coal in the coal pulverizer, preheating of the heating oil or similar) and then supplied in a controlled manner together with the combustion air to the combustion chamber in accordance with the current heat requirement of the installation. In this case the fuel is introduced into the firing chamber at different points of the steam generator at what are termed the burners. The air is also supplied at different points. A supply of air also takes place at all times at the burners themselves. In addition there can be supplies of air at points at which no fuel flows into the firing chamber.
The object is therefore to manage the combustion process in such a way that it executes in the most efficient manner possible with minimum wear and tear and/or with the lowest possible emissions. The typical key influencing parameters for the combustion process of a steam generator are:                Distribution of the fuel to the individual burners        Distribution of the combustion air streams to the different firing zones        Total mass air flow of the combustion air        Quality of the fuel preparation (e.g. pulverizing force, separator speed, separator temperature of the coal pulverizers)        Flue, gas recirculation        Position of swivel burners        
These influencing parameters are usually set at the time of commissioning of the steam generator. At this time, depending on boundary operating conditions, various optimization targets are prioritized, such as maximum plant efficiency, minimum emissions (NOx, CO, . . . ), minimum carbon content in the ash (completeness of the combustion). However, constant monitoring and adjustment of the combustion process is necessary due to the variability of the process parameters over time—in particular the fluctuating properties of the fuel (calorific value, air requirements, ignition behavior, etc.). In industrial installations the combustion is therefore monitored by means of measurement instrumentation and the available influencing parameters are modified by means of closed-loop control interventions in accordance with the currently detected combustion situation.
However, the influencing parameters are varied only to a very limited extent during operation of the plant. The reason for this is that due to the high temperatures, as well as the environment that is characterized by high levels of chemical and mechanical attrition, only few measurement results of adequate quality or even none at all are available from the immediate combustion environment. As a consequence only measured data recorded in the flue gas path far away from the combustion can be called upon for regulating the combustion. The process data is therefore available only with a delay and without specific reference to the individual actuating elements for closed-loop control optimizations. Furthermore, owing to the large dimensions of large-scale firing plants the available point measurements are often not representative and fail to reflect a differentiated picture of the real spatial process situation.
Since in many cases no closed-loop control or optimization of the combustion process is possible, the process parameters (e.g. excess air) are set at a sufficient distance from the technical process limits. This causes losses due to operation at a reduced level of process efficiency, higher levels of wear and tear and/or higher emissions.
A possibly present closed-loop control and optimization of the combustion process is performed according to the present prior art using different approaches:                Regulation of the total mass air flow based on a measurement of the oxygen content in the flue gas flow.        Regulation of the ratio between combustion air and top air based on a NOx and where necessary CO measurement in the flue gas flow.        In coal-fired boilers the supplied mass fuel flow is measured as the rotational speed of the metering hopper conveyor belt by means of which the coal is delivered to the coal pulverizer. In this case the precise apportionment of the coal flow to the burners supplied by said pulverizer is often not registered. It is therefore assumed that each burner carries a fixed percentage of the mass fuel flow and adjusts the combustion air accordingly. However, there exist a variety of measuring systems with the aid of which the coal flows of the individual burners can be recorded. A more precise regulation of the air wherein the mass air flow per burner is adjusted to the corresponding mass coal flow is therefore made possible.        In boilers equipped with a windbox the mass air flow per air supply is also not known initially. In order nonetheless to be able to perform a regulation of the air per air supply, the pressure differences across the individual dampers are recorded using measurement instruments and the mass air flows calculated from said measured data. In this way it is in turn possible to carry out a more precise regulation of the mass air flows that is geared to the fuel.        Neural networks are used to learn the relationship between the different influencing parameters and the measured process data. An optimization of the combustion process is then carried out on the basis of the thus resulting neural model of the steam generator.        A “method and control loop for controlling a combustion process” is defined in patent application EP 1 850 069 B1, wherein images of the combustion process at the burners are acquired and used to train neural networks with the aid of which an optimization of the combustion is then carried out.        In order to offset the large spatial extensions of the large-scale firing plants, some important process variables, such as the oxygen concentration in the flue gas, are recorded by means of grate measurements at the boiler outlet. This enables deductions to be made to a limited degree concerning the spatial distribution of the process variables in the combustion process.        
An even more extensive optimization of the combustion is made possible if a spatially resolving measurement system is used with the aid of which measured data from the immediate vicinity of the combustion can be made available.